Seattle authorities declared a state of emergency and called out National Guard troops after the first day of the World Trade Organisation was disrupted by anti-free trade activists.

The protesters blocked major intersections around the meeting sites of the 135-nation WTO, preventing motorcades for UN secretary general Kofi Annan and US secretary of state Madeleine Albright from making it to the opening session.

A handful of official delegates who made it through the demonstrators and acrid smell of tear gas milled about for several hours in the ornate theatre until WTO officials finally gave up and cancelled the opening speeches.

A surprised administration official conceded late on Tuesday night that the protesters may have won the opening round of the four days of discussions. But he vowed that President Bill Clinton would succeed in seizing the agenda today with a major speech highlighting the benefits of tearing down trade barriers.

"The president is very much looking forward to his visit here, to speaking to the people of Seattle, to the people of the United States," Gene Sperling, the president's chief economic adviser, told reporters at the WTO site late Tuesday night.

The Clinton administration has pushed for the WTO to consider environmental and worker safeguards when trade agreements are negotiated. But more than 100 of the WTO's 135 member nations are developing countries who have vowed to adamantly resist including these items in the upcoming round of global negotiations expected to be launched at these meetings.

Police fired tear gas and red pepper spray at roving bands of protesters throughout the day and well into the night. The goal after dark appeared to be clearing out a huge safety zone around the WTO sites and the hotel where the US president was staying.

President Clinton picked Seattle to host the event because no other state in the country owes as many jobs to international trade - one of three - thanks in part to exporting giants Boeing and Microsoft.

Washington Governor Gary Locke said he decided to call in as many as 200 unarmed members of the National Guard and up to 300 state troopers to provide relief to weary Seattle police.

"It's really critical that that we provide some relief for local law enforcement, many of whom have been on duty for more than 24 hours," the governor told reporters.

By late Tuesday, police said there had been 25 arrests.

 Forty people were arrested in demonstrations in London timed to coincide with the Seattle trade summit last night.

A police van was set alight and an officer injured in clashes with the police outside Euston station during the evening rush hour.

A Scotland Yard spokesman said there were 40 arrests from the Euston demonstration, mainly for public order offences, offensive weapons, violent disorder, threatening behaviour and affray.

"We condemn the actions of this violent minority which marred the otherwise peaceful demonstrations which took place," said the Yard spokesman.

One protester, Beatrice Stonemore, 21, said she and fellow activists had been cornered by more than 100 officers as they protested outside Euston station.

"I admit that we caused some damage but what do you expect when we were provoked by so many military-style police officers who were not interested in any form of peaceful demonstration."